It boils down to less unsprung weight (mass not supported by the suspension) that allows the suspension to react quicker to impacts, with another plus being that the fork's lubrication oil is likely to spend more time around the seals and bushings, thereby keeping the fork running smooth.

" Why would X-Fusion, among others, pursue an inverted design, especially when it presents such a design challenge? It boils down to less unsprung weight (mass not supported by the suspension) that allows the suspension to react quicker to impacts, with another plus being that the fork's lubrication oil is likely to spend more time around the seals and bushings, thereby keeping the fork running smooth. "

Can anyone explain to me why all motocross bikes use inverted forks but mtb uses standard? I'm a mechanical engineer but this has me stumped. My buddy that rides both says Honda came out with a standard MX fork once but then everyone complained it was too flexy!?!?

Can anyone explain to me why all motocross bikes use inverted forks but mtb uses standard? I'm a mechanical engineer but this has me stumped. My buddy that rides both says Honda came out with a standard MX fork once but then everyone complained it was too flexy!?!?

Just guessing...maybe cause MTb has only recently had thru axle type connections. Couldn't do inverted with old style 9mm bicycle dropouts.

Just guessing...maybe cause MTb has only recently had thru axle type connections. Couldn't do inverted with old style 9mm bicycle dropouts.

Good guess, but this can't be it. Fox had a prototype inverted DH fork that Aaron Gwin had been spotted doing practice runs on at World Cup races. Here maybe 6 months ago though they made an official announcement saying they were abandoning development citing excessive flex as the reason.

The larger diameter stanchions on motocross bikes allow for extra stiffness. There have been many attempts at inverted mtb forks, but larger riders still complain of flex. If someone makes a stiff USD fork, it would take over.

Assuming this fork ever makes it to production, I would be very surprised if it doesnt come with stanchion guards similar to what comes on the Manitou Dorado or White Brothers Groove. I would think they just kept them out of the picture to give a better look at the fork.

Its long been said that to make a bicycle USD fork stiff enough(twisting wise), for larger riders and extremely aggressive riders, a larger diameter axle would be required. Manitous 20mm Hex axle is suppose to be the best thing at 20mm, but still suffers from some flex. At this point, nobody wants to make a 25mm axled fork that comes with a hub. They dont feel the market is big enough to have the inconvenience.

Just guessing...maybe cause MTb has only recently had thru axle type connections. Couldn't do inverted with old style 9mm bicycle dropouts.

Marzocchi were doing 20mm inverted Shivers in 2002, they were great forks relative to what else was available (like Psylos...) but did suffer from left-right twisting. Mine didn't, but I was 14 and weighed bugger all, big guys could get visible flap out of them.

My guess is X Fusion have taken the keyed stanchions from the HiLo post and applied them to the inverted fork. If one little stanchion can resist twisting at the saddle, then two bigger ones bolted together should have no problems at the front wheel. As long as they stay in the uppers and avoid the wiper seals that should solve any twist issues.

Another issue so far with USD forks being stiffer is the weight. They are already heavier than most big forks on the market and to get a stiffer fork, you will need to either find a killer design or use stronger, but heavier materials and structure. And I'm pretty sure an inverted motocross fork weights a lot more than any MTB fork already. But I'm pretty sure they're gonna come up with something good one day, as carbon fiber, titanium, magnesium and other superior materials are being used in better ways and designs.

Originally Posted by NicoleB28

topless. that's what all mtb girls do. we go ride, get topless, have pillow fights in the woods, scissor, then ride home!

There's a reason every USB single crown fork has failed in the bicycle market. Without a second crown the fork cannot be made stiff enough without making it weigh a ton. Aside from that you're still dealing with more easily damaged stanchions and less wear/damage tolerant seals. Then at the end of the day the benefits from going USD on a bicycle are questionable.

On a motorcycle weight doesn't matter nearly as much and USD forks can be beefed up to be stiff enough. You can also run tighter and better seals since the weight of the motorcycle makes it more tolerant of stiction.

I really like X-Fusion, but it makes me sad they're wasting their resources on a evolutionary dead end.

There's a reason every USB single crown fork has failed in the bicycle market. Without a second crown the fork cannot be made stiff enough without making it weigh a ton. Aside from that you're still dealing with more easily damaged stanchions and less wear/damage tolerant seals. Then at the end of the day the benefits from going USD on a bicycle are questionable.

On a motorcycle weight doesn't matter nearly as much and USD forks can be beefed up to be stiff enough. You can also run tighter and better seals since the weight of the motorcycle makes it more tolerant of stiction.

I really like X-Fusion, but it makes me sad they're wasting their resources on a evolutionary dead end.

But they look so coooooooool

I've become a fan of X-Fusion stuff, but I am also a bit concerned about heading down this path. They already make good stuff that is way cheaper than the competition. Why not just go head-on into the DH scene with a traditional fork. There are no shortage of poor downhillers who will appreciate the value.

You can't say they have all failed since a couple companies still make USD mtb forks. You can't say weight for motorcycles doesn't matter either. People spend hundreds of dollars on TI bolts for motocross bikes just to save a pound. The flex issue is real though, and its caused by the stanchions being able to twist inside the uppers. If x fusion had found a way to solve this, and they sound confident that they did, it could be a great step forward. Anyone who has ridden on a USD fork loves the feel they give, other then the twisting of course.

You can't say they have all failed since a couple companies still make USD mtb forks. You can't say weight for motorcycles doesn't matter either. People spend hundreds of dollars on TI bolts for motocross bikes just to save a pound. The flex issue is real though, and its caused by the stanchions being able to twist inside the uppers. If x fusion had found a way to solve this, and they sound confident that they did, it could be a great step forward. Anyone who has ridden on a USD fork loves the feel they give, other then the twisting of course.

I said every single crown USD fork has failed, and they have. All the successful ones are dual crown, because the second crown is critical to making it stiff enough. A motorcycle, and motorcycle rider, is much more tolerant of an extra couple pounds on a fork considering the added performance, while on a bicycle an extra 100g is unacceptable.

I said every single crown USD fork has failed, and they have. All the successful ones are dual crown, because the second crown is critical to making it stiff enough. A motorcycle, and motorcycle rider, is much more tolerant of an extra couple pounds on a fork considering the added performance, while on a bicycle an extra 100g is unacceptable.

My bad, I read it on my phone and some how missed "single crown"

I still disagree on the weight issue though. 4.3lbs is very light. Lyriks and a regular vengeance is close to 5lbs. Even if it was 100g more, I dont think that would be unacceptable if it performed well.

I'm only guessing, but would it be possible that X-Fusion will put something similar needle bearing that Leftys have? Probably it's enough to put this kind of tech to the air/brake side and it will solve all issues that may come from the single crown and "only" 20mm thru-axle design.
I'm looking forward for more info about the tech of this USD fork.

But on a bike where both stanchions are connected by the thru axle and receiving forces from the same point is there any independent compression to prevent at all?

I don't ever recall seeing it on motos, or even Dorados and Shivers. Twisting and fore-aft bending always seem to be the bug bears on mtb forks, especially the latter.

Particularly since the spring and damper are in different legs, yes. But it's not a problem. a well designed 20mm axle is plenty burly enough to handle it. As has been noted, twisting is the biggest issue with an inverted fork, especially a single crown. The keyed stanchion thing should help there.

I dont think independent leg compression is much of an issue. Its more about the stanchions spinning in the uppers that is the problem. Keying them would make a huge difference, but would make sealing them a problem.

I will be very interested to read about the tech that they are using to help solve the problem. The Vengeance is one of the stiffest 160mm forks out right now. If the people at X fusion say its comparable, I am going to give them the benefit of the doubt. A Lyrik is pretty flexy in comparison to a Vengeance, so even if this new fork is similar in stiffness to a Lyrik, it would be plenty stiff for most people.

I don't think stanchion spinning is much of an issue. First, you have the thru axle to prevent that, and it is much stiffer than the torsion traveling down a long length of tube. Second, this stanchion spinning is accompanied by one fork leg moving forwards and one backwards. (The twist that happens when you turn the handlebars but the wheel doesn't turn.) So there is another mechanism to prevent this motion anyway. Third, for stanchion keying to prevent this motion, it will basically have to have zero play and no excessive drag. With all that said, my guess that they will be keyed anyway just so the fork doesn't go loopy when you take off the wheel. But I doubt it has any other structural purpose.

As for independent leg compression, the only thing prevent that on this fork is the clamping mechanism of the thru axle, bolted or press fit or glued to the end of a thin-wall stanchion. It will be easy to test just by grabbing the rim and fork leg together in one hand and squeezing.

Lets be honest here, Its not like its a measurable amount of twisting that happens. The honest reality of the situation is that its a combination of a small amount of stanchion spinning and a small amount of individual leg compression that gives USD forks there inherent twisting issue. Having a through axle is obviously helping the situation, but it doesn't solve the stanchion twisting issue completely. When enough force is applied, its still going to give way and give that little bit of flex that USD fork are known for. Axles are also only as stiff as the mounting system used allows. In the motocross industry, they use bigger axles among other things to solve the flexing issue. Manitou uses to shape of the axle to make the stiffest(so far) USD fork available.

The article speculates that only the top part of the stanchion is keyed, which would solve the seal issue. It also talks about how the stanchion being keyed(which would be the first of its kind) would solve most of the flexing issues. As of now its all just speculation though. Lets hope they produce it so we can learn more about what they did.

Isn't Paul Turner of Maverick Bikes now in league with X-Fusion? I love my DUC32 forks for trail duty.

And Maverick's all had proprietary hubs as well...

"Its long been said that to make a bicycle USD fork stiff enough(twisting wise), for larger riders and extremely aggressive riders, a larger diameter axle would be required... At this point, nobody wants to make a 25mm axled fork that comes with a hub. They dont feel the market is big enough to have the inconvenience." -Mullen119

As long as they stay with a hub that a hope pro can convert to, it's all good

I would like to know if this fork fits a 4" fat tire....they were being tight lipped & won't tell me on e-mail....wish someone had a measuring tape lol. I know it's only a prototype right now, but dammit tell me how wide it is!

"Its long been said that to make a bicycle USD fork stiff enough(twisting wise), for larger riders and extremely aggressive riders, a larger diameter axle would be required... At this point, nobody wants to make a 25mm axled fork that comes with a hub. They dont feel the market is big enough to have the inconvenience." -Mullen119

Well, even with the 24mm axle on my DUC there is a good amount of twist, but as stated above the mounting system plays a key roll.

I think it will take more than a large axle alone to deal with independent stanchion rotation and telescopic movement to mitigate twisting. Thatís what makes this new effort intriguing.

If keyed stanchions combined with a 20mm thru axle get the job done it would be great, otherwise the day may come when a new front axle standard hits the scene if stiff, long travel USD forks are to become a reality.